Utilisation of animal manures and sewage sludges for growing vegetables

Activated sludge, digested sludge, chicken manure and pig manure were used as soil additives for the growth of a local vegetable, flowering Chinese Cabbage, Brassica parachinensis. Edaphic properties of the waste-amended soils were measured. It was found that animal manures supported better growth than sewage sludges. Vegetables treated with animal manures had higher productivity, earlier maturity, absence of anatomical abnormalities and lower heavy metal contents. Application of chicken manure to agricultural land is a common practice of the local farmers. However, pig manure produced higher yields of the vegetable than chicken manure. This indicated that pig manure also has a high potential as a fertiliser. Recycling of pig manure is highly essential as some of the streams in the New Territories of Hong Kong are grossly polluted by pig manure.

The inferior growth of the vegetables harvested from sewage sludge amended soils was correlated with the edaphic properties of the sewage sludge amended soils. Such soils were lower in pH, conductivity and extractable phosphate, but higher in heavy metal content. Because of the high uptake of heavy metals in the sludge-grown vegetables, it is suggested that sewage sludge should be used as a soil additive only for non-edible crops. Furthermore, caution should be taken if crops like carrots were planted, due to the higher uptake of heavy metals in the root portion. Copyright © 1983 Applied Science Publishers Ltd, England.